This invention relates to announcement systems and, more particularly, to such systems which provide flexible system control.
In the past, recorded announcements have been provided via stand-alone equipment containing stored voice messages that were connected to the switch via an analog line or trunk. The messages have been stored in analog form on magnetic media (such as a tape or magnetic drum) or, in one recent case, the analog message signal from the switch has been digitally encoded and stored in the announcement equipment. In all cases, control of the announcement equipment has been limited by the sophistication of the signalling that can be done via an analog line or trunk.
In the most limited case, the announcement equipment appears as a conventional telephone to the switch. Thus, when the switch is directed to connect a customer to an announcement, it "calls" the announcement equipment. The announcement equipment, in response to the incoming call from the switch, answers the call and plays the announcement. When attached to a trunk, the switch can signal the announcement equipment to start playing a message by using trunk signalling techniques, e.g., winking or flashing, or seizing, the trunk to notify the equipment when to start playing the announcement.
In the most sophisticated case, the equipment still appears like a conventional telephone but, when the equipment answers the call, it accepts multi-frequency (MF) signalling from the switch to control the announcement. In most cases, however, each separate announcement requires a separate piece of announcement equipment and a separate line, or trunk, to the switch. More advanced announcement equipment has been designed to store more than one announcement, but they still associate one storage area with each announcement, e.g., equipment with four announcements requires four separate areas on a recording medium. Therefore, the announcement playback scenarios are limited in complexity to whatever capabilities the switch has for connecting a single fixed announcement to a call.
Another problem with existing systems is the fact that, even when multiple messages are possible, each message must be recorded in a prescribed manner. Some systems allow only a fixed number of messages, with each message using no more than a certain memory storage capacity. Other systems allow a variable number of messages but, because of the fixed nature of the memory storage arrangement, a changed message must be no longer than the message it replaced. In these systems, a change in one message usually requires a change in the other messages. Also, since the message must be stored in a fixed format, there is no opportunity to compress the message and thus gain greater memory capacity for other messages. In addition, using the systems currently available, it is not feasible to play the same announcement concurrently to different stations, particularly when the start times for each such station are different.